Concrete without Cement – A Green Alternative Fly Ash

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Concrete without cement is possible with the use of fly ash as an alternate for cement. It matches both the chemical and physical properties of cement. Thus it has the ability to replace cement completely. The word "concrete" defines as the bonding between aggregates, cement and water.  Concrete is the most common material used for construction due to its properties such as strength, durability and easy availability. But cement is commonly and necessary material used in preparation of concrete. Cement has excellent binding property but its production requires large amount of energy which contributes for pollution and global warming. The process of cement production starts from mining for raw materials, crushing, blending and heating these materials at high temperature of 1500⁰C and finally creating cement from heated materials. All the process involved in manufacturing of cement requires large amount of energy, it involves huge costs, contributes to increase in CO2 emissions and other greenhouse gases. The production of cement contributes to 7% of the emissions of greenhouse gases and it is likely to double by the year 2014. As the demand for more and more infrastructures is increasing day by day, the quantity of cement requirements is also increasing. With this, the control the emissions of greenhouse gases cannot be reduced to prevent global warming. To overcome this global problem and save the environment, a green alternative material is discovered - Fly ash

What is Fly ash ?

Fly ash is the by product obtained in the combustion of coal to generate electricity.  It is a waste product and has no other use in power plants. The use of flyash also reduces the energy demand of cement plants as well as reduces the space required for its dumping thus reducing the environmental impact of both cement concrete construction and thermal power plants. Typically fly ash is replaced by 25% of Portland cement in concrete to get good strength and durability. The property of flyash produced depends on type of coal being used in power plants, nature of combustion process. And the flyash properties suitable for use in cement can be used for concrete construction. Research at various places in the world has found that concrete in which cement was replaced with flyash, the concrete without cement offered exceptional performance in short term and long term strength of concrete and its workability relative to use of ordinary Portland cement concrete.

Advantages of Fly ash  Concrete:

• Fly ash concrete attains its ultimate strength quickly ,can be used for manufacturing precast members.
• Fly ash concrete does not generate any deleterious alkali-aggregate reaction even in the presence of high alkalinity.
• Fly ash concrete  has very low creep and shrinkage.
• Fly ash concrete can withstand heat and cold better than OPC cement concrete .
• Fly ash concrete cost analysis shows that it is economic than OPC cement concrete.

Disadvantages of Fly ash Concrete:

• Fly ash concrete requires external heat for curing.
• The polymerisation reaction is sensitive to many factors so the products lack uniformity.
• Fly ash concrete requires skilled labour for its batching and mixing.
• Fly ash concrete is still under study and research.

Adaptability of Fly Ash Concrete

The below table shows research done on  the adaptability and properties if tradition and fly ash concrete.